Recently, UV-curing compositions have been widely used because of their suitability for resource- and energy saving, higher operability, higher productivity, etc. In the field of processing printed boards, also, UV-curing compositions have been becoming used in place of conventional thermosetting compositions used for various inks such as solder resist inks and marking inks, for the same reason. The solder resist inks have first come to be prepared by use of UV-curing compositions.
The use to which the UV-curing compositions are applied at present, however, is limited to the field of the so-called civil-use boards used in radio receivers, video recorders, TV sets, etc., and application of the UV-curing compositions to the field of the so-called industrial-use boards for computers, control apparatus, etc. has not yet been made This is because the solder resist inks to be used for the industrial-use boards are required to have high performance as to electrical insulation properties, solder heat resistance under humid conditions, plating resistance, etc., which are not required for the solder resist inks for the civil-use boards, and the solder resist inks available for the civil-use boards at present have not yet reached the level of the performance requirements. Due to the recent trend toward smaller size and higher functionality of electronic equipment and apparatus, the requirement for higher accuracy of circuit pattern density in the industrial-use boards also has become severe, and the screen printing process using the conventional UV-curing solder resist inks has not yielded a satisfactory result, because of the limitations of accuracy of printing.
Besides, the conventional UV-curing solder resist inks contain mono- to trifunctional monomers such as 2-hydroxyethyl methacrylate, trimethylolpropane triacrylate, etc. and various acrylate oligomers, etc., and these substances may bleed out on screen printing, to cause troubles such as failure in adhesion of the solder. There have been attempts to improve the above-mentioned difficulties. For instance, Japanese Patent Application Laid-Open (KOKAI) No. 60-208377(1985) proposes a resin composition comprising a photopolymerizable epoxy vinyl ester resin, a photopolymerization initiator and an amine-based epoxy hardener Though the resin composition is excellent in heat resistance, adhesion properties, chemical resistance and electrical insulation properties, the composition has drawbacks in that the storage stability is poor due to the use of the amine-based epoxy hardener, and there is need for development with a solvent.